1. Field of the Invention
The present invention relates to a liquid crystal display (LCD), and more particularly to a liquid crystal display with a wide view angle.
2. Description of the Prior Art
The advantages of the liquid crystal display (LCD) include lighter weight, less electrical consumption, and less radiation contamination. Thus, the LCD have been widely applied to several portable information products, such as notebooks, PDAs, etc. The LCD gradually replaces the CRT monitors of the conventional desktop computers. The incident light will produce different polarization or refraction when the alignments of these liquid crystal molecules are different. The LCD utilizes the characteristics of the liquid crystal molecules to control the light transmittance and produce gorgeous images. However, the view angle of the conventional LCD is limited by the structure of the liquid crystal molecule and the optical character. Thus, it is necessary to develop a LCD with wider view angle.
Please refer to FIG. 1 and FIG. 2. FIG. 1 is the schematic diagram of the twisted nematic (TN) liquid crystal display 10 in the bright state according to the prior art. FIG. 2 is the schematic diagram of the twisted nematic LCD 10 in the dark state according to the prior art. As shown in FIG. 1, the TN-LCD 10 includes an upper substrate 12, a bottom substrate 14 in parallel and opposite to the upper substrate 12, an upper electrode 16 positioned on the upper substrate 12, a lower electrode 18 positioned on the lower substrate 14, two polarizers 20, 22 respectively positioned above the upper substrate 12 and the lower substrate 14, and a plurality of anisotropic liquid crystal molecules 24 with the positive dielectric constant filled in the space between the upper substrate 12 and the lower substrate 14. The polarized direction P1 of the polarizer 20 is parallel to the paper surface, and the polarized direction P2 of the polarizer 24 is perpendicular to the paper surface. The arrangements of the liquid crystal molecules 24 from the top to the bottom are changed from the direction parallel to the paper surface to the direction perpendicular to the paper surface.
As shown in FIG. 1, when no voltage is applied between the upper electrode 16 and the lower electrode 18 of the LCD 10, the liquid crystal molecules 24 are not affected by any electric field, and are parallel to the polarizers 20, 22, respectively. A light (not shown) is entered from the bottom and polarized after passing through the polarizer 22. The direction of the polarized light is perpendicular to the paper surface, and the polarized light can pass through the lower substrate 14. Next, the polarized light follows the direction of the liquid crystal molecules 24 and the direction of the light is gradually changed from a direction perpendicular to the paper surface to a direction parallel to the paper surface. Finally, the polarized light can pass through the upper substrate and the bright state of the TN-LCD 10 is formed because the direction of the polarized light is parallel to the polarized direction of the polarizer 20.
As shown in FIG. 2, an electric field 26 is produced between the upper substrate 12 and the lower substrate 14 when a voltage is applied between the upper electrode 16 and the lower electrode 18. The liquid crystal molecule 24 has a positive dielectric constants so the longitudinal axis of the liquid crystal molecules 24 align in parallel to the direction of the electric field 26, and also align perpendicular to the upper and lower substrates 12, 14. Thus, the direction of the light passed through these liquid crystal molecules is perpendicular to the polarizer 20 and no light can pass through the polarizer 20 so that the observer located above the upper substrate 12 is unable to see light. Therefore, the dark state of the TN-LCD 10 is formed.
Usually, there is a pre-tilt angle (not shown) formed between the liquid crystal molecules 24 and the upper substrate 12 or the lower substrate 14 for lowering the threshold voltage of the TN-LCD 10 and easily rotating the liquid crystal molecules 24 influenced by the electric field 26. However, the pre-tilt angle results in asymmetry of the liquid crystal molecules 24 and different light intensities under different view angle. Thus, the TN-LCD 10 has a limited view angle of display. In the TN-LCD 10, only a part of the liquid crystal molecules 24 located in the center space between the two substrates 12, 14 can rotate perpendicular to the substrates 12, 14. The other parts of the liquid crystal molecules will be at an angle to the substrates 12, 14 due to the adhesion force between the liquid crystal molecules 24 and the substrates 12, 14. Moreover, when the above mentioned pre-tilt angle effect Is considered, the liquid crystal molecules 24 under dark state do not arrange so uniform according to FIG. 2. The performance of the dark state is poor and the contrast of the LCD 10 is decreased. Furthermore, the view angle of the TN-LCD 10 is small, even the left view angle is different from the right view angle.
It is an objective of the present invention to provide a liquid crystal display having wide view angle.
The present invention provides a liquid crystal display. The display includes a first substrate having a first surface, and a second substrate having a second surface being in parallel and opposite to the first surface. A pixel area is defined on the second surface. The display further includes a first electrode positioned on the first substrate, a pixel electrode positioned on the pixel area of the second substrate, a first slit positioned on the pixel electrode along a first direction, and a plurality of negative liquid crystal molecules positioned between the first electrode and the pixel electrode. The longitudinal axis of the liquid crystal molecules are positioned along a second direction horizontally. A first angle is formed between the second direction and the first direction. When a voltage is applied between the first electrode and the pixel electrode, a biased electrical field is formed such that (a). a first horizontal biased electric field is formed near the first slit, and is perpendicular to the first direction to rotate the liquid crystal molecules and make the longitudinal axis of the liquid crystal molecules near the first slit rotate in parallel to the first direction, (b). the longitudinal axis of the liquid crystal molecules near the first electrode maintain in the second direction because no horizontal biased electrical field is formed near the first electrode; (c). the liquid crystal molecules between the first electrode and the first slit gradually rotate from the second direction to the first direction.
It is an advantage of the present invention that the liquid crystal molecules In the LCD have a smaller pre-tilt angle, so that the light flux passing through the liquid crystal molecules will not be affected when viewing from different positions. Therefore, the LCD of the present invention has larger view angle, and resolves the problem about the asymmetry of the left and right view angles in the prior art.